1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and in particular to a shield blocking electromagnetic field leakage from the PDP case and simultaneously allowing heat dissipation therethrough.
2. Description of the Related Art
A PDP, as shown in FIG. 1, displays an image when gas in its picture cells selectively becomes ionized under a certain voltage and thus generates ultraviolet light which collides with phosphor material 17 coating the walls 13 of the cells that emits visible light. The cells are defined by space between walls 13, between the front substrate 16 and rear substrate 10. In order to drive such a PDP high voltage driving signals are applied to electrodes 11, 14, and 15 embedded in dielectric layers 18 and 12 on the substrates 16 and 10 and a circuit board 30, disposed on the outside of the rear substrate as shown in FIGS. 2 and 3 and having a plurality of electrical/electronic elements such as semiconductor chips, resistors and capacitors, to take a few examples, generates the driving signals. Reference numeral 19 indicates a protective layer.
Because of a concern that electromagnetic field unavoidably generated from such circuits may be harmful to humans exposed to it, an electromagnetic (EM) shield 40 has been placed over the circuit board 30 to prevent EM fields from escaping from a case enclosing the electrical/electronic circuits. However, because electrical circuits also generate substantial heat, the shield must be removed for a proper operation of a device.
Conventionally a plurality of holes 41 were made in an EM shield as shown in FIG. 2 and FIG. 3 so that the heat can be dissipated through the holes. However, due to the provision of such holes 41 in the shield 40, sufficient protection against EM field leakage has not been possible.
It is an objective of the present invention to provide heat dissipation apertures in an EM Field shield and yet prevent leakage of EM through the apertures that would otherwise have happened.
In order to attain the objective, the present invention employs a multi-layered shield, where each of a plurality of preferably metal layers, spaced apart from each other, has apertures that are overlapped by shielding strips of an adjacent layer.